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      D 2 Dopaminergic Receptors: Normal and Abnormal Transduction Mechanisms

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          Abstract

          Dopamine receptors of D<sub>2</sub> type present on lactotroph cells are coupled to a large series of transduction mechanisms. Beside their negative coupling with adenylate cyclase, they are also coupled with potassium and calcium channels, leading to a decreased intracellular calcium concentration. In addition, D<sub>2</sub> dopamine receptors also modulate phospholipase activities. Dopamine inhibits inositol phosphate production, through two distinct mechanisms. One of them could represent a direct negative coupling with phospholipase C. All these transduction mechanisms of the D<sub>2</sub> dopamine receptors implicate G proteins sensitive to pertussis toxin. In contrast, these receptors are negatively coupled to phospholipase A<sub>2</sub> through G proteins insensitive to this toxin. Both isoforms of the D<sub>2</sub> dopamine receptor, generated by alternate splicing of a single gene, are present in lactotroph cells. After transfection in CH<sub>4</sub>C<sub>1</sub> cells the two isoforms are coupled with adenylate cyclase while only the shortest isoform appears negatively coupled to phospholipase C. Functional D<sub>2</sub> dopamine receptors are present in human prolactinomas. Resistance to bromocriptine therapy is associated with a decreased density of these receptors in the tumor. In addition, the ratio of the two receptor isoforms (measured by PCR) is different in responsive and resistant tumors. Furthermore, the activity of Gi/Go proteins coupled to adenylate cyclase appears also affected in resistant tumors. Resistance to bromocriptine therapy appears thus to involve multiple changes at the different levels of the multiple mechanisms of action of dopamine on lactotroph cells.

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          Author and article information

          Journal
          HRE
          Horm Res Paediatr
          10.1159/issn.1663-2818
          Hormone Research in Paediatrics
          S. Karger AG
          978-3-8055-5784-9
          978-3-318-01952-0
          1663-2818
          1663-2826
          1992
          1992
          03 December 2008
          : 38
          : 1-2
          : 78-83
          Affiliations
          aU. 159 INSERM, Paris; bU. 297 INSERM, UER Médecine Nord, Marseille, France
          Article
          182494 Horm Res 1992;38:78–83
          10.1159/000182494
          1306522
          © 1992 S. Karger AG, Basel

          Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

          Page count
          Pages: 6
          Categories
          Hormonal Resistance Syndromes

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